No, covering the soil won't work - they like the dark. Nematodes is your answer. Treat in late summer autumn when the larvae hatch.
see:
http://ladybirdplantcare.co.uk/vine_weevil.html

Whilst I consider myself 95% organic, Buddlejagar, I use chemical treatment for these devils. Provado Vine Weavil Killer watered onto the soil in the pots will kill existing grubs and this is probably a good time to do it.

I think the temp needs to be above 60 F for it to work.

Well I find a good inch of gritty sand on the top of pots does stop Vine Weevil larvae - they only seem to lay eggs on clear soil. I did that to all my pots last autumn and not found any this year, God willing. The adults like warm spots to hide in, so on evenings check garden walls, greenhouses and cold frames for them as well as their favourite plants (they seem to like Primroses but will try anything).